1. Field of the Invention
The present invention relates to a power semiconductor module with a semiconductor device such as a power device mounted therein and, more particularly, to a structure of a mounting frame for forcing the semiconductor module into pressure contact with an external heat sink.
2. Description of the Background Art
FIG. 9 is a cross-sectional view of a background art semiconductor module 118 shown as mounted on an external heat sink 111. The semiconductor module 118 comprises: an insulating substrate 117 including a ceramic plate 101, a first metal plate 102 and a second metal plate 103; a semiconductor device 105, such as a power device, mounted on the first metal plate 102 with solder 106; a case 104 having inside electrodes 109 connected through wires 107 to the semiconductor device 105 or the first metal plate 102, the case 104 being made of a thermoplastic resin such as polyphenylene sulfide (PPS) and polybutylene terephthalate (PBT); a resin 108 enclosed and cured in the case 104; and a cover 110 for the case 104.
After silicone grease is applied to a surface of the second metal plate 103 for enhancement of a heat dissipating property, the case 104 and the external heat sink 111 are fastened by screws 112, whereby the pressing force of the case 104 brings the insulating substrate 117 into pressure contact with the external heat sink 111.
In such a background art semiconductor module, the insulating substrate is forced into pressure contact with the external heat sink by the pressing force of the case, and the case is made of a thermoplastic resin. Thus, the case is gradually deformed by creep when used, in particular, continually in a high-temperature environment, and the pressing force of the case exerted upon the insulating substrate decreases with time. As a result, poor contact between the second metal plate and the external heat sink degrades the heat dissipating property.
A first aspect of the present invention is intended for a semiconductor module mountable on an external heat sink. According to the present invention, the semiconductor module comprises: an insulating substrate for the semiconductor module, the insulating substrate including a substrate, a first conductive pattern formed on a first main surface of the substrate which is on the opposite side from the external heat sink, and a second conductive pattern formed on a second main surface of the substrate which is on the same side as the external heat sink and for contact with the external heat sink; and a mounting frame made of metal and having a mounting surface for contact with the external heat sink, the mounting frame including a flange along a periphery thereof for engagement with a peripheral part of the insulating substrate at the first main surface, the flange pressing the peripheral part of the insulating substrate toward the external heat sink to force the insulating substrate into pressure contact with the external heat sink.
Preferably, according to a second aspect of the present invention, in the semiconductor module of the first aspect, the mounting frame further includes: a first metal plate having the mounting surface; and a second metal plate disposed on the first metal plate and having a protrusion along a periphery thereof projecting from a periphery of the first metal plate to define the flange.
Preferably, according to a third aspect of the present invention, in the semiconductor module of the second aspect, the thickness of the first metal plate is equal to the sum of the thickness of the substrate and the thickness of the second conductive pattern. The thickness of the second metal plate is equal to the thickness of the first metal plate.
Preferably, according to a fourth aspect of the present invention, in the semiconductor module of any one of the first to third aspects, the insulating substrate further includes a third conductive pattern formed on the first main surface along a periphery of the substrate. The flange and the insulating substrate contact each other, with the third conductive pattern therebetween.
Preferably, according to a fifth aspect of the present invention, in the semiconductor module of the fourth aspect, the third conductive pattern is formed partially to allow part of the flange to contact the third conductive pattern. The mounting frame and the insulating substrate are bonded to each other with an adhesive filling a gap between part of the flange which is out of contact with the third conductive pattern and the first main surface.
Preferably, according to a sixth aspect of the present invention, in the semiconductor module of any one of the first to third aspects, the substrate, the first conductive pattern and the second conductive pattern of the insulating substrate have respective peripheries in alignment with each other. The flange presses the periphery of the first conductive pattern toward the external heat sink, with an insulative material between the flange and the first conductive pattern.
Preferably, according to a seventh aspect of the present invention, the semiconductor module of any one of the first to sixth aspects further comprises: a semiconductor device mounted on the first conductive pattern; a cylindrical case disposed on a main surface of the mounting frame which is on the opposite side from the external heat sink; the case, the mounting frame and the insulating substrate defining a space surrounding the semiconductor device; and an insulative sealing material filling the space.
Preferably, according to an eighth aspect of the present invention, in the semiconductor module of the seventh aspect, the sealing material is a thermosetting resin.
A ninth aspect of the present invention is intended for an insulating substrate for a semiconductor module. According to the present invention, the insulating substrate comprises a mounting surface, the mounting surface being adapted to be forced into pressure contact with an external heat sink by a mounting frame pressing a peripheral part of the insulating substrate, the insulating substrate having a curved configuration in which a peripheral part of the mounting surface warps upwardly away from the external heat sink above a central part of the mounting surface.
In accordance with the first aspect of the present invention, the insulating substrate for the semiconductor module is forced into pressure contact with the external heat sink by the pressing force of the metal mounting frame, rather than a conventional case made of a thermoplastic resin. This causes no creep, to avoid the problem of a decreasing pressing force resulting from the deformation of the frame even after continual use in a high-temperature environment. Consequently, the semiconductor module can ensure a satisfactory heat dissipating property over a long period of time.
Additionally, the metal frame has a better heat dissipating property than the conventional case made of the thermoplastic resin. This achieves the size reduction of the semiconductor module.
The production of the flange of the mounting frame by pressing requires various types of manufacturing management such as the management of a pressing tolerance and the management of the flatness of the mounting frame. On the other hand, in the case of the semiconductor module in accordance with the second aspect of the present invention, the management of only the tolerance of the thickness of the first metal plate is required. This facilitates the manufacturing management.
Further, the semiconductor module in accordance with the second aspect of the present invention eliminates the need to machine the flange by pressing to achieve the increase in productivity and the reduction in costs.
In accordance with the third aspect of the present invention, the thickness of the first metal plate is equal to the thickness of the second metal plate. This further facilitates the manufacturing management.
In accordance with the fourth aspect of the present invention, the flange and the insulating substrate contact each other, with the third conductive pattern therebetween. This provides further enhancement of the heat dissipating property and further size reduction of the semiconductor module.
Additionally, the semiconductor module in accordance with the fourth aspect of the present invention can insure uniform stresses applied from the flange through the third conductive pattern to the substrate, suitably preventing cracking in the substrate.
In accordance with the fifth aspect of the present invention, the adhesive may be made as thick as the third conductive pattern. Thus, if a resin in gel form is used as a sealing material for covering a semiconductor device, the adhesive prevents the sealing material from flowing out, providing the highly reliable semiconductor module.
In accordance with the sixth aspect of the present invention, the size of the insulating substrate is reduced in accordance with the elimination of an overhang extended outwardly from the periphery of the first conductive pattern. The size of the semiconductor module itself is accordingly reduced.
In accordance with the seventh aspect of the present invention, the insulative sealing material filling the space provides a mechanical strength and ensures insulation between the metal mounting frame and the semiconductor device.
In accordance with the eighth aspect of the present invention, the insulating substrate is prevented from being broken by an external force applied from the direction of the second conductive pattern, before the semiconductor module is mounted on the external heat sink.
In accordance with the ninth aspect of the present invention, when the peripheral part of the mounting surface is forced into pressure contact with the external heat sink by the mounting frame for the mounting of the insulating substrate on the external heat sink, the central part of the mounting surface is also necessarily brought into pressure contact with the external heat sink. Thus, the ninth aspect of the present invention ensures better contact between the insulating substrate and the external heat sink particularly at the central part of the mounting surface, accomplishing further enhancement of the heat dissipating property.
It is therefore an object of the present invention to provide a semiconductor module and an insulating substrate therefor which can avoid the problem of a decreasing pressing force resulting from deformation to ensure a satisfactory heat dissipating property over a long period of time.
These and other objects, features, aspects and advantages of the present invention will become more apparent from the following detailed description of the present invention when taken in conjunction with the accompanying drawings.